The present invention relates to the beneficiation of ore. More particularly, the present invention relates to the beneficiation of titaniferous ores that contain iron through leaching.
Naturally occurring titanium ores are the raw materials for many commercial products. For example, naturally occurring rutile titanium dioxide ore is a raw material for pigment for paper, coatings, and plastics products. Unfortunately, this type of ore is scarce and expensive to use as a feedstock.
Ilmenite ore is another type of naturally occurring ore. It is an attractive alternative to naturally occurring rutile titanium ores because it is both cheaper to mine and more common. Unfortunately, ilmenite and many other naturally occurring ores often contain unacceptable levels of certain impurities that render them undesirable for use in industrial processes without some degree of purification. In the case of ilmenite, the ore contains mostly unacceptable levels of iron.
A number of processes have been suggested for removing impurities from ores such as ilmenite and making them more suitable for industrial applications. For example, slagging, partial chlorination, and the Becher process are currently being used to beneficiate ilmenite ore.
One may also upgrade ilmenite by removing its iron oxide content, as well as many other impurities through acid leaching. Examples of such acid leaching processes are the Benilite process and the Ishihara process. Both of these processes are well known to persons skilled in the art. Commercially, the upgraded TiO2 feedstock material produced through leaching processes is referred to as “synthetic rutile.”
Acid leaching of titanium oxides is a well known method for purification. However, conventional acid leaching has two shortcomings. First, often it is desirable to remove a greater percentage of the impurities than is practical under current technologies without increasing other parameters such as leach intensity and retention time, which increase both capital and variable costs. Second, acid leaching often generates a large amount of acid waste.
In order to develop acid leaching processes that yield sufficiently pure TiO2 products, many persons have used pretreatment steps in connection with complex leaching methods that require both multiple Teachings and magnetic separation of the partially leached ore from the ore particles that have been completely leached. The phrase “leached ore” refers to ore that has had one or more constituents removed through the use of a leaching agent. Further, in some cases it is necessary to include a seeding step in order to facilitate leaching of the ore. These steps all have costs associated with them that become significant when they are performed on an industrial scale. For example, one needs to obtain a sufficient amount of the leaching agent. Additionally, even using these added steps, it is often difficult to generate a sufficiently pure titanium dioxide product economically.
Moreover, any process for acid leaching will need to address the handling of acid waste by-products. Most current technology calls for either the neutralization and disposal of waste solids from such processes or for a high temperature roasting process, which produces metallic oxides and acid. Both of these types of processes render current acid leaching techniques to be of limited economic attractiveness.
Most known acid leaching of ores that contain titanium oxides has focused on the use of hydrochloric acid. However, for both of the aforementioned reasons—the costs for developing a sufficiently pure product and the disposal of waste being too high—processes using hydrochloric acid have been less than ideal for acid leaching. Thus, it is necessary to explore leaching techniques that use other acids, as well as to develop ways to increase the efficiency of the overall process.
Sulfuric acid has been tried as an alternative, but to date has not been viewed as a success, in part because many prior attempts have not generated high enough yields of sufficiently pure titanium oxides, and have generated large amounts of waste. In fact, absent a pretreatment step, sulfuric acid leaching of ilmenite results in a product that differs only marginally from the starting ilmenite in terms of TiO2 and iron oxide content. Further, in those processes that have suggested pretreatment steps, the steps have not been optimized in order to generate a product that is easy to process during leaching. Instead, the prior attempts have required the additional aforementioned use of costly magnetic separation and/or seeding steps.
For the above reasons, the development of a cost-effective beneficiation process that reduces waste is needed. The present invention provides both an efficient means to beneficiate certain ores through a sulfuric acid leaching process, as well as to increase the efficiencies of these processes by separating and recycling this acid from what have traditionally been viewed as waste water streams.